Yes, 100m is confusing, what it really means is it was tested in a pressurised water filled tank to a equivalent depth in still cold water. In reality if you were at that depth, the current and your arm movement etc would make the pressure way way past 100m. When i used to sell watches i used to think of it like this: 30m resistant = splash proof and surface water smimming. 50m = bottom of a pool etc..... There is a test for divers watches, that does mean you can use its stated water resistance and you used to get a certificate pass.
The only watch with similar features sold by Garmin is the Descent MK1 which is very similar to the 5x but with a dive computer added. You can push the buttons underwater with that watch.
Look for watches with a rating of ISO 6425 if you want a “divers” watch.
Pushing it occasionally or by accident underwater won't likely cause a problem. But one of the commonalities about water compromised watches on this forum is that many did not know about that warning. Water gets trapped between the button and seal as mentioned above, causing pressure on the seals underwater (it spills out above water). Repeatedly doing so compounds the risk.
